Diabetic retinopathy (DR) is an eye disease that develops in diabetes due to changes in the cells that line blood vessels, i.e. the retinal microvascular endothelium. During diabetes mellitus, hyperglycemia can cause damage in a number of ways. For example, glucose, or a metabolite of glucose, binds to the amino groups of proteins, leading to tissue damage. In addition, excess glucose enters the polyol pathway resulting in accumulations of sorbitol. Sorbitol cannot be metabolized by the cells of the retina and can contribute to high intracellular osmotic pressure, intracellular edema, impaired diffusion, tissue hypoxia, capillary cell damage, and capillary weakening. Diabetic retinopathy involves thickening of capillary basement membranes which may in turn prevent pericytes, the predominant perivascular cell type in retinal capillaries, from contacting endothelial cells. Pericyte and endothelial cell death occurs through an apoptotic mechanism during diabetic retinopathy, where the loss of pericytes likely increases the permeability of the capillaries and leads to breakdown of the blood-retina barrier and blood flow dysregulation. Weakened capillaries lead to aneurysm formation and further leakage. These effects of hyperglycemia can also impair neuronal functions in the retina. DR is associated with retinal microaneurysms, hemorrhages, exudates, and retinitis proliferans, i.e., massive neovascular and connective tissue growth on the inner surface of the retina. Diabetic retinopathy may be of the background type, progressively characterized by microaneurysms; intraretinal punctate hemorrhages; yellow, waxy exudates; cotton-wool patches; and macular edema. This is an early stage of diabetic retinopathy termed nonproliferative diabetic retinopathy.
As the diabetes-induced microvascular pathology progress, retinal capillaries eventually become occluded and lead to multifocal areas of ischemia hypoxia within the retina. Hypoxic conditions in the non-perfused tissue causes an increase in HIF-1α levels. The resulting changes in HIF-1-mediated gene expression elicits the production of growth factors capable of stimulating abnormal new blood vessel growth from existing vessels (angiogenesis). These pathologic new blood vessels grow into the vitreous and can cause loss of sight, a condition called proliferative diabetic retinopathy (PDR), since the new blood vessels are fragile and tend to leak blood into the eye. The proliferative type of DR is characterized by neovascularization of the retina and optic disk which may project into the vitreous, proliferation of fibrous tissue, vitreous hemorrhage, and retinal detachment.
Neovascularization also occurs in a type of glaucoma called neovascular glaucoma in which increased intraocular pressure is caused by growth of connective tissue and new blood vessels upon the trabecular meshwork. Neovascular glaucoma is a form of secondary glaucoma caused by neovascularization in the chamber angle.
Posterior segment neovascularization (PSNV) is a vision-threatening pathology responsible for the two most common causes of acquired blindness in developed countries: exudative age-related macular degeneration (AMD) and PDR. Until recently, the only approved treatments for PSNV that occurs during exudative AMD were laser photocoagulation or photodynamic therapy with VISUDYNE™. Both therapies involve occlusion of affected vasculature, which results in permanent, laser-induced damage to the retina, and does not address the underlying cause of neovascularization. Recurrence of neovascularization from the same area is common. For patients with PDR, surgical interventions with vitrectomy and removal of preretinal membranes are the only options currently available, as well as a laser therapy called panrctinal photocoagulation to prevent the production of more new vessels.
Current pharmaceutical efforts have focused on inhibiting the effects of potent angiogenic factors such as VEGF, a gene that is regulated by HIF-1. Recently, intravitreal injection of LUCENTIS™, an anti-VEGF antibody fragment, was approved for treatment of AMD. This antibody fragment was designed to bind to and inhibit VEGF to inhibit the formation of new blood vessels. Lucentis is also in clinical trials for the treatment of diabetic macular edema. Other approaches include the use of small interfering RNA targeting VEGF or its receptor.
Disruption of the interaction between the HIF-1 transcription factor and the hypoxia response element in oxygen sensitive promoters using conventional small molecule inhibitors is likely to be very difficult. Like VEGF, HIF1A is not considered to be “druggable” in the classical sense. Furthermore, the silencing of individual downstream effectors of HIF-1, such as VEGF or RTP801, may only partially block neovascularization.
The present invention addresses the above-cited problems and provides interfering RNAs targeting HIF1A, the transcriptional control gene for downstream genes involved in angiogenesis and vascular permeability (edema).